A number of unsaturated alcohols possess desirable organoleptic properties which make them useful in the preparation of flavor and fragrance intermediates. One such compound is the cis-isomer of 3-hexen-1-ol or "leaf alcohol" which possesses a pleasant, green aroma characteristic of new-mown grass. Originally, the compound was extracted from the leaves of green plants, but soon after the structure was determined, a synthetic procedure for the preparation of cis-3-hexen-1-ol was discovered and commercialized.
The starting material for the present day manufacture of cis-3-hexen-1-ol is butyne-1. The unsaturated alcohol was first synthesized by reacting butyne-1 with sodium or lithium in liquid ammonia to prepare butynylsodium, which was further reacted with 1,2-epoxyethane and hydrolyzed to yield the 3-hexyn-1-ol. This intermediate was then hydrogenated over palladium catalyst to yield the corresponding cis-3-hexen-1-ol. Due to its unavailability and low demand, butyne-1 is a very costly starting material. Thus, the economics of the production of the cis-3-hexen-1-ol is relatively expensive.
As hereinafter described, it is necessary to employ an unsaturated aluminum alkyl compound as an intermediate. The process for manufacturing these unsaturated aluminum alkyl intermediates has been previously reported. However, it has been found in practice that these unsaturated aluminum alkyl intermediate compounds are relatively unstable with respect to isomerization and decomposition, especially at higher temperatures. Thus, these prior art processes have proved to be unsatisfactory.